Searching for a book with Hades as the lead sent me down quite the rabbit hole. Most of what you'll find falls into the 'romantasy' or modern retelling category, especially with the huge popularity of 'Persephone' retellings on TikTok and BookTok. The challenge is that while many books feature Hades, he's not always the singular, central protagonist. A lot of popular ones are told from Persephone's perspective or alternate between the two.
That said, if you're specifically after that brooding, underworld-king energy front and center, Scarlett St. Clair's 'A Touch of Darkness' series flips the script a bit; it's primarily told from Persephone's POV, but Hades gets significant page time and his own novellas. I've seen a lot of chatter about Katee Robert's 'Neon Gods,' which is a very spicy, modern Olympus-set erotic romance where Hades is absolutely a main character, though it's a duet narration with Persephone. For something older, try 'Goddess of Spring' by P.C. Cast—a lighter, body-swap romance where Hades is a central figure.
Honestly, I ended up browsing through the 'Hades & Persephone' and 'Greek Mythology Retelling' shelves on Goodreads, filtering by 'male protagonist' tags. The niche is growing, but you have to sift through a mountain of Persephone-first narratives to find the ones that truly give Hades the narrative reins.